The present invention relates to a scroll-type compressor and, more particularly, to an improvement in the construction of the fluid inlet passage in a scroll-type compressor.
In general, an electrically driven hermetic compressor of scroll type has a compressor section and an electric motor section which are hermetically sealed in a closed vessel. The fluid passages in this type of compressor, therefore, extend through the wall of the closed vessel to external equipment such as an evaporator and a condensor in a refrigeration system. The compressor section includes a scroll-type compressor essentially having a stationary scroll member and an orbital scroll member which are assembled together with their wraps meshing with each other. The wraps of the scroll members are formed along an involute curve or a curve resembling an involute curve so as to extend upright from the end plates of respective scroll members. The suction port for the fluid is formed to open outside but near the area of the confined spaces formed between meshing wraps, while the discharge port is formed near the center of the stationary scroll member. An Oldham's ring, preventing the orbital scroll member from rotating around its own axis, is disposed between the orbital scroll member and the frame or between the orbital scroll member and the stationary scroll member. A crankshaft is connected through a bearing to the orbital scroll member so that, as the crankshaft is driven, the orbital scroll member makes an orbital movement without rotating around its own axis. This orbital movement causes a change in the volume of the closed chambers formed between two wraps of the scroll members thereby to progressively compress the fluid confined in such chambers. The compressed fluid is discharged to the outside of the compressor through a dicharge valve connected to the discharge port. In order to efficiently compress and discharge the gas, it is essential that the orbital scroll member is adequately pressed against the stationary scroll member in the axial direction. This axial pressing force is produced by the difference between the pressure of the gas acting in the compression chamber and the pressure acting on the back side of the orbital scroll member. The pressure acting on the back side of the orbital scroll member is produced by the gas which is introduced through a small communication hole providing a communication between the compression chamber and the back side of the orbital scroll member.
Additionally, bearings, sliding parts and compressor section of this type of compressor are cooled by a lubricating oil which is maintained in the closed vessel. More specifically, the lubricating oil is drawn up through an oil passage bore formed through the crankshaft and delivered to bearings due to the difference between a high pressure and an intermediate pressure. The lubricating oil is then supplied into a back-pressure chamber formed behind the orbital scroll member. The lubricating oil introduced into the back-pressure chamber is then relieved to the compression chamber through the communication hole at a suitable rate and is mixed with the gas under compression so as to be recirculated together with the gas.
A typical example of the electrically-driven hermetic scroll-type compressor of the kind described above is shown in, for example, Japanese Patent Laid-Open No. 73886/1982.
In this type of compressor, the discharge valve is adapted to be closed when the compressor stops operating, in order to prevent reversing of the orbital scroll member due to a reversing flow of the compressed fluid. As this discharge valve is closed, the equilibrium state of pressure is established between the interior of the compressor and the low-pressure side of the system to which the compressor is connected, so that the lubricating oil, which has been forcibly fed by the differential pressure, is undesirably allowed to flow back to the suction side through the communication hole. Consequently, only a small amount of lubricating oil is left in the oil reservior within the closed vessel and, hence, it is often experienced that the bearings and other sliding parts are burned due to insufficient lubrication soon after a re-start of operation of the compressor. The relief of the lubricating oil to the low-pressure side would be avoided if the discharge valve is omitted because, by so doing, a high pressure is maintained in the compression chamber even after the stopping of the compressor. However, the elimination of the discharge valve causes another problem: namely, a reversing of the orbital scroll member accompanied by unfavorable reversing noise. The problem of noise caused by the reversing of the fluid is encountered also in screw-type refrigerant compressors. In order to avoid this problem, Japanese Patent Publication No. 3803/1983 proposes a screw-type compressor having check valves disposed in the suction and discharge pipes. In this screw-type compressor, the suction-side check valve disposed in the suction pipe is spaced considerably from the compression chamber of the compressor, so that the low pressure is left in an ample space even after the closing of the suction-side check valve. This proposal, therefore, cannot satisfactorily overcome the problem of relief of the lubricating oil to the suction side which may lead to a decrease in the amount of oil residing in the oil reservoir of the closed vessel and a consequent insufficient lubrication.